Display panel or portion thereof with a graphical user interface



The sole FIGURE is a front view of a display panel or portion thereof with a graphical user interface showing a design.

The broken line showing of the display panel or portion thereof with a graphical user interface and portions of the graphical user interface form no part of the claimed design. 

CLAIM The ornamental design for a display panel or portion thereof with a graphical user interface, as shown and described. 